With the progress in the miniaturization, larger capacity, high performance of electric devices using semiconductors, the amount of heat generation from the semiconductors mounted therein with a high density is ever-increasing. For example, in order for a central processing unit of a personal computer or a semiconductor device used for controlling a motor of an electric vehicle to be operated stably, a heat sink or a radiator fin for heat dissipation is indispensable, and therefore, as a member which connects the semiconductor device with a heat sink or the like, a material which can have insulation properties and thermal conductivity in combination is demanded.
In general, for an insulating material such as a printed board which contains a semiconductor device or the like, an organic material is widely used. Although such an organic material has high insulation properties, it has a low thermal conductivity, and therefore does not have large contribution to heat dissipation of a semiconductor device or the like. On the other hand, an inorganic material such as an inorganic ceramics may be used for heat dissipation of a semiconductor device or the like. Although such an inorganic material has a high thermal conductivity, its insulation properties are far from satisfactory compared with those of an organic material. A material having high insulation properties and a thermal conductivity is thus demanded.
In connection with the above description, many studies are under way about a composite material of a resin and an inorganic filling agent having a high thermal conductivity which is referred to as “filler”. For example, an epoxy resin composition which has a low melt viscosity and is capable of attaining a high filling rate of a filler is known (for example, see Japanese Patent Application Laid-Open (JP-A) No. 2001-055425). It is reported that a cured material having a complex system of a common bisphenol A epoxy resin and an alumina filler is known, which can attain the thermal conductivity of 3.8 W/mK in xenon flash method, and the thermal conductivity of 4.5 W/mK in thermal wave analysis (for example, see JP-A-2008-13759). Similarly, it is reported that a cured material having a complex system of a special epoxy resin and an amine curing agent and an alumina filler is known, which can attain the thermal conductivity of 9.4 W/mK in xenon flash method, and the thermal conductivity of 10.4 W/mK in thermal wave analysis (for example, see JP-A-2008-13759).
It is reported that, as a cured thermosetting resin having a further excellent thermal conductivity, a thermally conductive resin composition containing boron nitride, and polymer components such as an epoxy resin, an amine curing agent, and a curing catalyst can attain the thermal conductivity of 6 W/mK to 11 W/mK in thermal wave analysis (for example, see JP-A-2008-189818).